The present invention relates generally to the field of test apparatus, and more particularly to apparatus for providing noninvasive assessment of properties of pressurized containers.
Articles formed of plastic materials are often used as containers for food, beverages, or the like, and such containers are generally designed to give certain performance properties. One function of packaging is to form a barrier against permeation of gasses to or from the food product. For example, reduction of the carbon dioxide permeation rate helps to maintain a high level of carbonation in carbonated beverages. Therefore, the choice of suitable plastic material is obviously important, as well as the distribution of material and the processing conditions, as is well known in the blow molding art.
A major difficulty with volume production of plastic containers is that periodic sampling of production containers is required to ensure that the container is performing to the desired specifications. In the prior art, the periodic sampling required actual, direct measurement of the physical property of interest. Some of the required measurements, however, are extremely painstaking and time consuming to perform. In the case of the carbonation retention, for example, the actual, direct measurement thereof requires a substantial amount of large test equipment and apparatus, including plumbing, precision gas detectors, etc. In addition, the decrease in carbonation level of a sealed container is so low that a test cycle usually lasts for several weeks, before an estimate of carbonation loss rate can be obtained for predicting the shelf life of a consumer product, such as carbonated beverages. Related to this are the physical and material properties of the container which effect and affect the carbonation retention capability of such containers.
Known prior methods require removing all or a portion of either the headspace gases, or the liquid, for analysis. Prior analysis techniques include (a) gas chromatography which involves separation and detection of gases; (b) conductometric titration which involves detection of dissolved ionic species, e.g. HCO.sub.3.sup.- ; (c) simple headspace pressure determination of all gases, non selectively; (d) the use of a CO.sub.2 -permeable pH probe; and (e) the use of infrared absorption in an external cell. None of these prior art methods contemplate direct examination of an intact, capped, pressurized plastic container that has been filled with a product under pressure and then sealed, to determine the concentration of at least one gas in the headspace of such container.
Accordingly, a need exists for a faster, simpler method for providing nondestructive carbonation-retention monitoring and performance prediction in beverage containers. Moreover, it would be desirable to be able to quickly predict the processing effects on materials properties and to evaluate container-to-container variation.